Conventionally, there has been known an ultraviolet irradiation apparatus that includes: a treatment tank through which treated water passes; a UV irradiation member that is provided inside the treatment tank and irradiates treated water passing through the inside of the treatment tank with UV light; and a UV sensor that is provided inside the treatment tank and measures a dose of UV irradiation from the UV irradiation member.
In such a conventional UV irradiation apparatus as described above, air (air bubbles) contained in treated water may accumulate inside (in a top part of) the treatment tank when the treated water passes through the inside of the treatment tank. When such accumulation has occurred, a UV light receiving surface of the UV sensor may be exposed in air as a result of accumulation of air between the UV sensor and the UV irradiation member. Consequently, the accuracy of UV irradiation dose measurement performed by the UV sensor is possibly impaired.
An ultraviolet (UV) irradiation apparatus according to an embodiment comprises a treatment tank, a UV irradiation member, a UV sensor, and an air outlet unit. The treatment tank comprises a water supply opening to supply therethrough treated water to be further treated and a water drainage opening to drain therethrough the treated water. The UV irradiation member is provided inside the treatment tank and irradiates the treated water with UV light when the treated water passes through inside of the treatment tank. The UV sensor is provided inside the treatment tank and measures a dose of UV irradiation from the UV irradiation member. The air outlet unit is connected to an air outlet hole provided at a position higher than a horizontal plane passing through the UV sensor, and is provided to release, to outside of the treatment tank, through the air outlet hole, air that accumulates inside the treatment tank when the treated water passes through the inside of the treatment tank.